1. Field of the Invention
This invention relates to an automated liquid sample analyzer having a fluid system for proportioning two liquids in highly reproducible volumes, with substantial independence with respect to the flow rates of such liquids.
2. Prior Art
In automated apparatus for quantitatively analyzing sequentially a series of samples of blood or other liquids for one or more constituents of interest, it has been common to proportion various liquids utilized in the analytical process by employing a proportioning unit comprising a peristaltic pump and a manifold including compressible pump tubes. This general type of apparatus is illustrated, for example, in Skeggs et al U.S. Pat. No. 3,241,432 issued Mar. 22, 1966. Such liquid porportioning has been highly dependent on flow rates in the various manifold tubes. The flow rates and the liquid proportioning have been subject to variations effected by such factors as changes in the effective diameters of the tubes, temperature and fluid viscosity for example. Changes in proportioning of liquids such as sample, diluent or reagent adversely affects the analytical results of such an automated analyzer.
It is also known that a shear valve has been utilized in an automated analyzer to provide a fixed-volume chamber for only a single liquid such as the sample to obtain a reproducible volume of such sample, the sample volume being displaced from the chamber toward an analysis station by a pilot fluid. One such apparatus is illustrated in Isreeli et al U.S. Pat. No. 3,583,232 issued June 8, 1971.
The present invention contemplates improved liquid proportioning in an automated analyzer.